Bipolar flow - Flujo bipolar
In the early stages of the formation of a small mass star, associated with the accretion of matter by the protostar , the expulsion of part of this matter is also observed in the form of protostellar jets / jets.
Protostellar jets play a very important role in the star formation process. In fact, these objects are believed to rotate, thereby assisting in the dissipation of angular momentum from the system, thus allowing material from the disk to be deposited on the surface of the star. Furthermore, these objects greatly influence the final mass of the protostar. This is because when they expand through the molecular cloud, they dissipate part of the material in the cloud, limiting the amount of matter that is deposited on the disk and in turn on the protostar. Thanks to the interaction of protostellar jets with the interstellar mediumwe can derive physical and chemical properties from the latter. Despite their great importance in the overall picture of star formation, very little is known about the evolution and formation of these objects.
According to their evolutionary stage the jets, and in general the young stellar objects, can be classified from Class 0 objects to Class III objects. This classification was originally proposed by Lada & Wilking (1984) [ 1 ] and was later modified by Andre et al. (1993) [ 2 ] to include previously unknown Class 0 objects.
Class 0 objects evolutionarily represent the youngest objects. In fact, in these systems the central protostar is still hidden due to the enormous amounts of gas and dust that surround it. That is why class 0 protostars are not observable in the optical and it is necessary to travel to wavelengths of the mid-far infrared to be able to detect these very young objects. The SED (from the English " spectral energy distribution " spectral energy distribution ) of objects class 0 is characterized by the emission of black bodyof the surrounding material. Class 0 objects are also characterized by a high rate of accretion, which entails the emission by the star of enormous amounts of matter. In general the jets associated with Class 0 objects are characterized by molecular emission, such as CO, H 2 O or H 2 . The typical material ejection rate of these underdeveloped objects is of the order of 10 -6 solar masses per year (M sun / yr). The next evolutionary stage is represented by Class I objects. At this stage, an accretion disk has already formed around the protostar. thick and the envelope has been reduced considerably but not enough for the central star to be optically visible.
- Lada & Wilking, ApJ, 1984, 287, 610-621
- Andre, P., Ward-Thompson, D. and Barsony, M., ApJ, 1993, 406, 122